Ethyldiphenylphosphine oxide

Deamination reactions of (2-amino-l,l-dimethyl)ethyldiphenylphosphine oxide (57) result in the formation of three products, in each of which the diphenylphosphinyl group has migrated to the primary carbon of the starting material. These reactions are unusual examples of non-assisted migration of a phosphinyl group. 

Yamashita, M., Tsunekawa, K., Sugiura, M., and Oshikawa, T., Novel preparation of diphenylphosphine oxides via direct deoxygenation of 1,2-epoxy-ethyldiphenylphosphine oxides, Synthesis, 65, 1985. 

Preparation of alkyldiphenylphosphine oxides. General procedure from phospho-nium salts. Triphenyl phosphine is heated under reflux with an excess of alkyl halide. The precipitated phosphonium salt is filtered off, washed well with ether, and then heated with 30 per cent w/w aqueous sodium hydroxide (c. 4 ml/g) until all the benzene has distilled out. The mixture is cooled and extracted with dichloromethane, and the extracts are dried (magnesium sulphate) and evaporated to dryness. In this way ethyldiphenylphosphine oxide is obtained from triphenyl phosphine (65.6 g, 0.25 mol) and iodoethane (42.9 g, 0.275 mol) in dry toluene (250 ml) to give first the phosphonium salt (102.4 g, 97.9%) after 3.5 hours, from which the phosphine oxide is obtained as needles (53.2 g, 92.5%), m.p. 123-124 °C (from ethyl acetate) p.m.r. 5 (CDC13, TMS) 1.9-13 (m, 10H, Ph2PO), 2.3 (m, 2H, CH2) and 1.2 (dt, 3H, JHm, = 7 Hz, JMeP = 17 Hz, Me). 

Ethyldiphenylphosphine oxide 397 Diphenylphosphinic acid (0.22 g) is converted into the acid chloride by 1-2 hours boiling under reflux with thionyl chloride (0.5 ml) in toluene. About half the solvent is then distilled off and the residual solution is diluted with benzene and dropped at room temperature into a Grignard solution prepared from magnesium (0.25 g) and ethyl bromide (2.5 ml). The reaction is complete after half an hour s boiling under reflux. The product is hydrolysed by ice and hydrochloric acid, the aqueous layer is washed with ether, and ether phases are united, dried, and evaporated. The residue is subjected to steam-distillation and then extracted several times with ether. The residue left on evaporation of these extracts crystallizes at once or on short storage and is decolorized in acetone by charcoal. Recrystallization from ether-light petroleum or aqueous acetone affords the oxide, m.p. 123-124° (67%). 

Ethyldiphenylphosphine, 2115(06115)2 , is obtained as a colourless, strongly refractive oil, B.pt, 203° ., having a pungent odour, and readily undergoing oxidation with formation of ethyldiphenylphosphine oxide. 

Ethyldiphenylphosphine oxide, (C2Hg)(C6H5)2TO, occurs when the phosphonium compound is treated with silver oxide as before, or can be obtained from ethyl diphenylphosphinite, (CgH5)2P.OC2H5, under the catalytic influence of ethyl iodide at room temperature. It separates from boihng ether in colourless, glistening prisms, M.pt. 121° C. 

The Hoffmann test has also been successfully used to investigate the configurational stability of lithiated diphenylphosphine oxides [113]. It was shown that they are not configurationally stable in tetrahydrofuran (THF) at —78°C on the timescale of their reaction with the aldehyde 193 used to perform the test (on lithiated ethyldiphenylphosphine oxide). 

C28H31CI2M0NO3P2, Dichlorobis(ethyldiphenylphosphine oxide)(imino)-oxomolybdenum, 45B, 1277... 

An unstable tri(perfluorophenyl)phosphine complex can be obtained by oxidative addition of chlorine to the dimeric rhodium(I) complex. The ethyldiphenylphosphine complex prepared in this way is more stable (equation 202). 

Caution. In common with other alkyldiarylphosphines, ethyldiphenylphosphine presents some hazard because of its toxicity and susceptibility to air oxidation. Therefore, all operations must be performed in an efficient hood with manipulations conducted under an inert atmosphere. All ground-glass joints should be greased thoroughly with a silicone lubricant. 

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